Global Regulation in Pseudomonas Syringae

Abstract

Two questions come rather quickly to mind when one is confronted with writing a chapter on global regulation in Pseudomonas syringae. The first of these is very basic, and goes to the eventual scope of the article: what is P. syringae? This is not a straightforward quest ion, as the species is something of a taxonomic mess. P. syringae has long been recognized as a member of the original “inner circle” of pseudomonads, eventually codified as the rRNA Group I47. This group was further refined by both general and molecular characteristics into two additional phylogenetic groupings recently described as the intrageneric clusters (IGC) I and II, with P. syringae being in IGC II63. Detailed analysis of the nucleotide sequences of the gyrB and rpoD genes indicated that the IGC II cluster could be reduced still further to three complexes, with one being the “P. syringae complex” containing the pathovars and nomenspecies traditionally associated with P. syringae63, After this point, the taxonomic picture becomes less clear. Plant pathogenic pseudomonads are not readily differentiated by standard phenotypic characteristics and have often been classified largely by host range as pathovars or subspecies of P. syringae53, This is an unusually heterologous grouping, with DNA hybridization studies, ribotyping, and general characteristics having defined at least six47, and possibly as many as nine17, discrete genomospecies within the complex.

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